function [ centers ] = get_4_tanget_spheres_centers( r )
%The function gets a radius, and returns the centers of 3 tangent
%circles around (0,0)
centers = zeros(4,3);
centers(1,:) = [ -r, r/sqrt(3), 0];
centers(2,:) = [r, r/sqrt(3), 0];
centers(3,:) = [0, -2*r/sqrt(3), 0];
centers(4,:) = [0,0,sqrt(8/3)*r];
